Yes, you read that right: on April 17, 2007, the Oklahoma State Senate passed a bill declaring that not only is watermelon a vegetable (related to cucumbers, they said), it's also the state's official vegetable. (Source)

I applaud Oklahoma's category-redefining efforts, which I have just (belatedly) discovered. More of this capricious sort of thing from our legislators might make me pay attention to politics: if I could turn on the news and find out California had renamed itself Atlantis or that the IQ of Canada's Prime Minister was now going to determine the value of its dollar ... the news might get turned on.

Fruit is a botanical and culinary term, vegetable is only a culinary term. In the botanical sense, a vegetable can be a fruit, a root, a fungi, a leaf... It is called a vegetable because of how it is used in the kitchen, not in the garden, therefore, I'm pretty sure a watermelon is not a vegetable.